Natural products show outstanding potential as starting point in drug discovery, especially in the quest for anticancer drugs. The research proposed here will explore structure-activity relationships of largazole, a marine natural product that shows nanomolar and selective antiproliferative activity against cancer cell lines in vitro. We will characterize the antitumor mode of action and assess the therapeutic potential of most promising largazole analogs. We recently discovered largazole during our ongoing program to find novel antitumor drugs from marine cyanobacteria. Our preliminary data indicate that largazole is a potent histone deacetylase (HDAC) inhibitor. HDACs have emerged as attractive targets for anticancer drug discovery since epigenetic gene silencing due to aberrant HDAC activity has been associated with several types of cancers; first-in-class HDAC inhibitor on the market Zolinza (Merck) was approved for the treatment of cutaneous T-cell lymphoma in late 2006. The working hypothesis tested is that largazole exerts its antitumor activity by class I HDAC inhibition, thereby selectively inhibiting cancer cell growth, and could be an effective drug against a variety of tumors in vivo. First, we will systematically explore two areas within the structure of largazole to complete our structure-activity relationship (SAR) studies, improve potency of HDAC inhibitory activity, and provide insights on the class I HDAC specificity of largazole. Second, we will examine the direct effects of synthesized largazole analogs on various HDAC isoforms and assess stability and metabolism. Third, we will determine transcriptional consequences of cancer cell treatment with various synthetic, bioactive largazoles and determine drug exposures necessary to achieve antitumor activity. Fourth, we will execute pharmacological and therapeutic efficacy studies with prioritized largazoles and address plasma stability, in vivo pharmacokinetics in tumor-bearing mice and ultimately carry out efficacy studies. PUBLIC HEALTH RELEVANCE: Selective inhibitors of the enzyme histone deacetylase could be promising anticancer agents. We have identified a lead compound from a marine cyanobacterium and we propose to synthesize a series of related compounds with improved selectivity and potency and test the efficacy of the most promising compounds in cancer cells and in mice tumor models.